The invention relates to telecommunications networks, and more particularly to restoration and normalization of a restored connection in a telecommunications network.
Rapid recovery/restoration from network failures is a crucial aspect of current and future telecommunication networks. Rapid restoration is required by transport network providers to support stringent Service Legal Agreements (“SLAs”) that dictate high reliability and availability for customer connectivity. For example, and in the context of optical networking, Synchronous Optical Network (SONET) rings provide the primary technology for optical layer communication and restoration from network failures. SONET rings tend to be capacity utilization inefficient when compared to “mesh” topologies in networks with a high degree of connectivity and when, because of size limitations, connections are forced to route through many interconnected rings. As optical-cross connects (OXCs) are deployed within today's transport networks based on wavelength-division multiplexing (WDM), the potential emerges to provide on-demand establishment of high-bandwidth connections (also referred to in the art as “lightpaths” or “label switched paths (LSPs)”). Emerging standards such as Generalized MPLS (“GMPLS”), also referred to in the art as Multi-Protocol Lambda Switching (“MPL(ambda)S”), can provide a standardized optical network control plane that is essential for building an effective platform for vendor interoperability. See, e.g., D. Awduche et al., “Multi-Protocol Lambda Switching: Combining MPLS Traffic Engineering Control with Optical Crossconnects,” IETF Internet Draft, http://www.ietf.org/internet-drafts/draft-awduche-mpls-te-optical-01.txt (November 1999). Unfortunately, few recent contributions to the art have addressed the need for fast failure restoration in such networks. GMPLS signaling proposals have primarily focused on the development of methods for label switched path (“LSP”) establishment and removal—with limited fault recovery capabilities. In this specification, we will use the common terminology “LSP” for connection in transport network.
The choice of a restoration policy is a tradeoff between network resource utilization (cost) and service interruption time. Clearly, minimized service interruption time is desirable, but schemes achieving this usually do so at the expense of network resource utilization, resulting in increased cost to the provider. Significant reductions in spare capacity can be achieved by sharing restoration capacity across multiple restoration paths whose service paths do not fail at the same time during independent failures. In co-pending commonly-assigned U.S. Utility patent application, “METHODS AND SYSTEMS FOR FAST RESTORATION IN A MESH NETWORK OF OPTICAL CROSS CONNECTS,” Ser. No. 09/474,031, filed on Dec. 28, 1999, which is incorporated by reference herein, a restoration methodology is disclosed that utilizes pre-computed restoration path disjoint from the normal service path—but wherein the channels/wavelengths may be chosen dynamically during the restoration process. The invention therein disclosed, referred to by the inventors herein generally as “shared mesh restoration”, can potentially provide restoration competitive with SONET ring restoration speeds. Co-pending commonly-assigned U.S. Utility patent application, “METHOD FOR SELECTING A RESTORATION PATH IN A MESH NETWORK,” Ser. No. 09/909,102, filed on Jul. 19, 2001, which is also incorporated by reference herein, discloses a distributed approach to selecting the restoration path in a shared mesh restoration scheme.